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I bought a 2008 tdi 2.0 few days ago . Was on motorway doing 70mph but speedo says im doing 100mph anyone any ideas as to what is causing the reading ???
 

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More info needed. What was the odometer telling you over known measured distances from signs to exits etc? If you play with the MFD options on the stalk, what distances and average speeds are they telling you compared to the high speedo readings. Are they consistent, telling lies or the truth? Are there any ABS warnings? When you first turn on the key, can you see the ABS warning light come on with all the others, then go off?
 

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70 based on....?
The camera ticket that came through the post. ;)? Looking at km/h? PO had a Euro speedo fitted for France? If cruise control is fitted set it to 70mph and time across a measured distance between signs or mile markers. Or do it using a watch on seconds and time the distance travelled between motorway signs at constant speed.
 

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No it was for the OP to answer.

If the 70 is true but its reading 100, I'd be looking at module 17, instrument cluster, not so much for fault codes but the coding.
 

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I agree. I did think about that, but the options are usually there to correct for different wheel and tire sizes and 70-100mph is such a large error I wouldn't expect adaptation to cover the range? Whilst the speedo itself gets the same impulses from the wheel sensors, it could be faulty. By doing the odo checks I suggested, if the odo is correct and the speedo isn't, that looks like a speedo instrument display fault. If both odo and speedo are consistently wrong, that suggests the tacho pulses from wheel sensors are wrong but I doubt adaptation would correct that much? If the ABS light has been disabled to hide an ABS fault, the wheel sensor pulses could be wrong which will affect both speedo and odo, although I would expect a lower than correct speed rather than such large high speed error. Cruise control if fitted uses the digital speed signals, which was another angle to my reply.

I have another newer VAG which I adapted to an Australia (I think) model . This gives the added feature of a large digital speed readout on the MFD which you can select on the stalk switch. This will cross check the dial speedo for accuracy. Also useful for drivers getting speeding tickets, because speeds can be anywhere from 27-35 on the cramped display, when the camera and laser is looking for >30mph excess speed. MY07 EOS has the basic low line MFD and I can't do the same.
 

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More info here:


Need to see what the OP says, really, though. With the right scan tool, you can see live data and there's about 137 different places you can read off the vehicle speed. Engine, transmission and ABS module would be the obvious starting points though.

A discrepancy of 100mph vs 70mph on a new car might just be down to some other unreliable comparison with eg a crappy phone app trying to do it off GPS and unfamiliarity with a (new to you) car. If it really exists, then I'd be looking at all the wheel speeds and comparing with the others in the other modules. If its a manual I don't know about coding in there though.
 
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